The objective of this project is to investigate information processing of temporal modulation by the auditory system. That is, the goal is to better understand the method and manner by which information conveyed by modulation is extracted and utilized. The proposed work focuses on three aspects of information processing of temporal modulation: complex modulation perception, modeling, and processing of the modulation in speech. Using detection, discrimination, and speech-intelligibility paradigms, the proposed experiments study both envelope and fine-structure modulation and also the interaction of the two time varying functions. To establish a context of sound-source processing for this study, proposed experiments evaluate the perception of complex patterns of modulation (a characteristic of real-world sources), use a source attribute as a response identifier in many procedures, and examine the effects on performance of the interaction among multiple sources of modulation information. Detection and discrimination experiments are designed to allow for direct evaluation of models of auditory processing of complex modulation. The speech studies are based on signal-processing algorithms that manipulate the modulation in speech. The intent of the speech studies is to both gain insight into the role of temporal modulation in speech perception and to suggest processing schemes that may enhance the performance of prosthetic devices. Specifically, speech results obtained with combined envelope and phase modulation may suggest approaches to compensate for the reduced dynamic range and spectral transposition of modulation information with cochlear implants. Multi-message conditions are studied to evaluate the extent to which modulation information can be segregated by source and still utilized in a meaningful way.